Recently, a see-through display device is a target of attention as a display device for information display or digital signage. Such a see-through display device allows the background (rear side of a display panel) to be seen through, and thus is capable of displaying information displayed on the display panel and the background in an overlapping manner. Therefore, the see-through display device has a splendid effect of appealing to potential customers and a splendid eye-catching effect. It has also been proposed to use the see-through display device for a showcase or a shop window.
In the case where a liquid crystal display device is used as a see-through display device, there is a bottleneck that the liquid crystal display device has a low light utilization factor. Such a low light utilization factor is caused by a color filter or a polarization plate provided in a general liquid crystal display device. The color filter and the polarization plate absorb light of a specific wavelength range or light of a specific polarization direction.
In such a situation, it is conceivable to use a liquid crystal display device of a field sequential system. In the field sequential system, the color of light directed from an illumination element toward a liquid crystal display panel is switched in a time division system to provide color display. Therefore, the color filter is not needed, and thus the light utilization factor is improved. However, the field sequential system requires a liquid crystal display device to have a high speed response.
Patent Document 1 and Patent Document 2 each disclose a liquid crystal display device having an improved response characteristic by including an electrode structure capable of generating a vertical electric field and a lateral electric field in a switched manner in a liquid crystal layer. In the liquid crystal display device disclosed in each of Patent Document 1 and Patent Document 2, a vertical electric field is generated in the liquid crystal layer in one of a transition from a black display state to a white display state (rise) and a transition from the white display state to the black display state (fall), and a lateral electric field (fringe field) is generated in the liquid crystal layer in the other of the rise and the fall. Therefore, a torque by voltage application acts on liquid crystal molecules in both of the rise and the fall, and thus a high speed response characteristic is provided.
Patent Document 3 also proposes a liquid crystal display device realizing a high speed response by causing an alignment control force, provided by an electric field, to act on the liquid crystal molecules in both of the rise and the fall.